Physical shadow masks are used in combination with thin film deposition techniques to pattern thin materials upon substrates. Very often, silicon is the substrate and the thin material is a metal, such as copper, or a dielectric, such as silicon dioxide. These patterns may serve optical functions (such as modifying the appearance of a substrate), electronic functions (such as modifying the dielectric constant of a material or forming electronic circuits), magnetic functions, or other functionality. Typically, the substrate is planar such as with silicon wafers and the physical shadow mask is also planar to match. The shadow mask is a single material which has apertures cut out of it to form a pattern. This pattern is the negative of the pattern which will be transferred to the substrate. It is important to have intimate contact between the shadow mask and the substrate so that the deposited material only deposits under the apertures in the mask and not under the solid portions of the mask. The materials may be conductors, such as metals, and the deposition may be by chemical vapor deposition (CVD) or by physical vapor deposition (PVD), such as sputtering or evaporative deposition.
Antenna designs such as the one disclosed in U.S. Pat. No. 8,922,452 offer superior properties to planar electrical circuits but cannot be economically manufactured on a commercial scale using existing methods. Several firms attempted the fabrication of this design without success.
In the prior art, physical shadow masks are fabricated using subtractive machining, such as milling or reactive ion etching. Such a mask is then attached to a substrate prior to metal deposition. Alternately, masks have been additively printed and then, prior to metal deposition, bridges have been added to make the masked features continuous, as taught by Isaac M. Ehrenberg, et al.
Isaac M. Ehrenberg, et al., used an additive manufacturing process that included a 3D printer to fabricate a paraboloid and a conformal mask on the surface of the paraboloid. Electron beam evaporation was then used to deposit copper, through apertures in the mask, onto the surface of the paraboloid. However, Ehrenberg's process deposits a film about 1.2 μm thick, which is relatively thick for an evaporative process, but is too thin for soldering. Furthermore, Ehrenberg's films are thinner than the skin depth of ultra-high frequency (UHF) signals, such as signals used in global positioning systems (GPS) receivers. The skin depth of such a signal in copper is about 2-5 μm, with a resistivity between about 1.68 and about 16.8 μOhm-cm. Ehrenberg's thin layer of deposited metal and, its high electrical resistance, therefore, does not satisfy many applications. Furthermore, the layer of deposited metal is too thin to be soldered.
Some electronic circuit fabrication techniques do not involve masks. For example, metallic inks have been omnidirectional printed directly on flexible, stretchable and curvilinear surfaces. However, with currently available technology, electrical resistivity of resulting circuits is several times larger than metallic bulk resistivity or thin film resistivity.